1. Field of the Invention
The present invention relates to a recording medium transportation apparatus incorporated in an image recording apparatus that performs image formation such as printing on a recording medium such as a sheet of paper. Particularly, the present invention relates to improvement of an apparatus using a belt drive device and generating suction force by air suction at the belt surface to transport a recording medium held on the belt by the suction force.
2. Description of the Background Art
Conventionally, printers and copy machines are known as the equipment of performing image formation such as printing on a recording medium such as a sheet of paper or film. A belt drive device is employed as the means to transport a recording medium in such equipment.
A general structure of an ink jet type printer transporting a recording medium using a belt drive device will be described hereinafter.
As shown in FIG. 13, this type of belt drive device includes a drive roller 101, a driven roller 102 and a tension roller 103. An endless belt 104 is extended around rollers 101, 102 and 103. Drive roller 101 is connected to a drive shaft of a motor not shown to rotate by the transmission of the drive force of the motor. Belt 104 runs in the direction of arrow A in FIG. 13 in accordance with the rotation of drive roller 101. Pinch rollers 105, 105 sandwiching belt 104 between drive roller 101 and driven roller 102 are provided at the upper area in FIG. 13 opposite to drive roller 101 and driven roller 102, respectively. A sheet cassette 106 is arranged in the proximity of driven roller 102. A recording medium (paper sheet) 107 output from sheet cassette 106 is transported in the direction of arrow A in accordance with the run of belt 104 while being sandwiched with belt 104 between driven roller 102 and pinch roller 105.
A printer head 108 is provided above the portion of belt 104 located between drive roller 101 and driven roller 102 (this portion of belt 104 is called xe2x80x9cspanxe2x80x9d 104a hereinafter). Printer head 108 is configured of the line type head or serial type head. A line type head includes a plurality of spray out nozzles corresponding to the resolution across the required printing width (for example, approximately 200 mm in printing out onto a A4-size paper sheet) in a direction perpendicular to the paper plane of FIG. 13. A serial type head includes several ten to several hundred of spray nozzles in the direction of A in FIG. 13 to effect printing on a recording medium 107 while moving in the direction perpendicular to the paper plane of FIG. 13.
In a printing operation, recording medium 107 is output from sheet cassette 106 in accordance with the drive of the belt drive device. Recording medium 107 is transported in the direction of arrow A in a status sandwiched with belt 104 between driven roller 102 and pinch roller 105.
In the case where printer head 108 is of the line type, ink is output appropriately from each spray out nozzle of printer head 108 while recording medium 107 is continuously transported. As a result, printing is effected on recording medium 107.
In the case where printer head 108 is of the serial type, the travel of belt 104 is temporarily halted when recording medium 107 is transported to the position where printer head 108 is disposed. Ink is output from the spray out nozzle while printer head 108 moves in the direction perpendicular to the paper plane of FIG. 13, whereby printing is effected on recording medium 107. When printer head 108 comes to one side end of recording medium 107, belt 104 begins to move again. After recording medium 107 is shifted by a predetermined distance, belt 104 stops again. The printing operation is recommenced while printer head 108 moves in the direction perpendicular to the paper plane of FIG. 13. Thus, the printing operation by printer head 801 and the operation of moving recording medium 107 by the belt drive device are carried out alternately to effect printing onto recording medium 107.
In this type of device, a configuration of drawing recording medium 107 towards belt 104 is employed to transport recording medium 107 stably on belt 104. More specifically, a platen chamber 109 is provided at the backside of span 104a of belt 104 located between drive roller 101 and driven roller 102. Platen chamber 109 has suction holes 110, 110, . . . formed at the top surface. Air suction is effected through suction holes 110, 110, . . . by setting the interior to negative pressure. Also, a plurality of suction holes (not shown) are formed at belt 104. Recording medium 107 is attracted to belt 104 by the air suction from the suction hole in accordance with the generation of negative pressure within platen chamber 109. Accordingly, position shifting of recording medium 107 on belt 104 is prevented to allow a stable transportation operation of recording medium 107.
In the following, the force suppressing recording medium 107 from floating or curling, i.e. the force to draw recording medium 107 is called xe2x80x9csuction forcexe2x80x9d whereas the holding force acting between recording medium 107 and belt 104 is called xe2x80x9cattracted forcexe2x80x9d, and distinction is made therebetween.
When the structure in which recording medium 107 adheres to belt 104 by air suction is employed, the total area of the suction holes covered by recording medium 107 becomes larger if the size of recording medium 107 transported on belt 104 is big enough. In other words, the total area of suction holes not covered by recording medium 107 (suction holes not contributing to attraction) becomes smaller. Therefore, the suction resistance at the suction holes of belt 104 becomes larger, so that a great suction force can be obtained. As a result, recording medium 107 adheres to belt 104 favorably to allow a stable transportation operation.
If recording medium 107 transported on belt 104 is small in size, the total area of suction holes covered by recording medium 107 becomes smaller. In other words, the total area of suction holes not covered by recording medium 107 becomes larger. There is a possibility that a stable transportation operation cannot be performed due to the smaller suction force.
Japanese Patent Laying-Open No. 6-135613 discloses a transportation apparatus directed to solve the above problem. This transportation apparatus is provided with a valve that opens/closes each suction hole of the platen chamber. Open/close control of the valve is provided so that only the suction holes corresponding to the passage of the recording medium are opened. Accordingly, a stable transportation operation of a recording medium can be carried out with a constant high suction force.
The conventional structure of holding the recording medium by air suction has been developed directed to only ensure a high suction force. No consideration was made as to the suction position.
When the suction hole of the belt is located at a position outside the side end of the recording medium, no suction force will be effected on the side end area. There is a possibility of this area will float upwards off the belt. In some cases, this portion may rise to be curled. Generation of such a curl induces the possibility that a printing operation will not be carried out satisfactorily due to the recording medium coming into contact with the printer head to be smudged or causing sheet jamming. This phenomenon is particularly significant in the case where a relatively small recording medium is transported that has the tendency of a lower suction force.
In the case of a serial type printer head, the deliver operation and halt operation of the recording medium are carried out alternately in the transportation operation of an apparatus including this type of head. High accuracy is required in the transportation amount of the recording medium. In order to achieve transportation of high accuracy, the side end of the recording medium must adhere to the belt reliably to prevent position shifting between the recording medium and the belt.
In view of the foregoing, an object of the present invention is to prevent generation of a curl in a recording medium and allow the recording medium to be transported at high accuracy in a recording medium transportation apparatus that transports the recording medium held adhered to the belt by air suction.
To this end, the suction hole of a belt formed to attract the recording medium by air suction is located facing the side end of the recording medium in the present invention. Generation of a curl is suppressed by the side end of the recording medium adhering to the belt.
According to an aspect of the present invention, a recording medium transportation apparatus includes a suction chamber drawing in air, and a transportation belt with a surface to transport a recording medium. A plurality of suction holes to introduce air into the suction chamber are formed at the surface of the transportation belt. At least a portion of the suction holes at the transportation belt is formed located opposite to the side end region of the transported recording medium to attract that side end region.
In the recording medium transportation apparatus that transports a recording medium held attracted on the belt by air suction of the present invention, the suction holes of the belt formed to attract the recording medium by air suction is positioned to face the side end region of the recording medium. Therefore, the side end region of the recording medium can be held against the belt in a favorable manner to prevent the recording medium from being curled upwards. By applying this recording medium transportation apparatus into an image recording apparatus, the problem that a favorable printing operation cannot be performed due to the recording medium coming into contact with the printer head to be contaminated or occurrence of sheet jamming can be eliminated. As a result, a stable image formation operation can be carried out to improve the picture quality of the image formed on the recording medium. Particularly in the case where a relatively small recording medium (post card or B5-size sheet) that has the tendency of smaller suction force is transported, the side end of the recording medium can be held towards the belt in a favorable manner to effectively prevent generation of a curl. The present invention can sufficiently respond to the demand for an image recording apparatus that includes a serial type printer head that must have the side end of the recording medium adhere to the belt reliably for the purpose of ensuring a transportation amount of high accuracy corresponding to the alternate operation of forwarding and stopping the recording medium. Position shifting between the recording medium and the belt can be prevented to improve the picture quality of the image that is formed on the recording medium.
Preferably, the recording medium transportation apparatus of the present invention further includes a roller to drive the transportation belt. The transportation belt is an endless transportation belt. This endless transportation belt has a span for the transportation of a recording medium. A plurality of suction holes are formed at the surface of the endless transportation belt. At least a portion of the suction holes of the endless transportation belt is formed at a position facing the side end region of the recording medium placed on the span to attract that side end region.
Preferably, the plurality of suction holes form a plurality of rows of holes arranged linearly substantially parallel to the transportation direction of the recording medium. Also preferably, the plurality of suction holes form a plurality of rows of holes arranged linearly substantially perpendicular to the transportation direction of the recording medium. Further preferably, the plurality of suction holes are arranged in a staggered pattern.
Preferably, at least a portion of the plurality of suction holes forms a row of holes arranged linearly so as to face the side end region of a recording medium located substantially parallel to the transportation direction of the recording medium placed on the span. Further preferably, a plurality of rows of holes are arranged parallel to each other so as to face the side end region of respective recording media of a plurality of sizes.
In this case, the side end of the recording medium parallel to the transportation direction can be held against the belt to prevent this side end from curling. Particularly in the case where a plurality of rows of holes are arranged so as to be able to correspond to respective recording media of different sizes, the above-described advantage can be provided for the recording medium of each size with the same belt. Thus, the versatility of the apparatus can be improved.
Preferably, the total opening area of suction holes of at least one row differs from the total opening area of suction holes of another row. Also preferably, the total opening area of suction holes of at least one row is larger than the total opening area of suction holes of another row. Further preferably, the total opening area of suction holes in respective rows becomes smaller as located closer to the outer side of the transportation belt in a direction substantially perpendicular to the transportation direction of the recording medium.
By the features of the present invention, appropriate suction force can be generated at each row of holes. Particularly in the case where the total opening area of suction holes of a certain row is set larger than the total opening area of suction holes of another row, the suction force of that certain row can be made larger than the suction force of holes of another row. When the total opening area of suction holes of respective rows is set smaller as a function of location closer to the outer side of the belt in the belt width direction, the total area of suction holes occluded by the recording medium can be set relatively large even when a relatively small recording medium is transported. Therefore, sufficient suction force can be generated. In the case where a relatively large recording medium is transported, sufficient suction force can be generated since this type of recording medium inherently has a large total area of suction holes occluded. Therefore, sufficient suction force can be obtained for a recording medium of any size.
Suction holes of a different size can be arranged alternately in at least one row of holes in the transportation direction of the recording medium.
Preferably, at least a portion of a plurality of suction holes forms a row of holes arranged linearly so as to face the side end region of a recording medium located substantially perpendicular to the transportation direction of the recording medium placed on the span. Also preferably, at least a portion of the plurality of suction holes forms a row of holes arranged linearly so as to face the side end region of the leading edge in the transportation direction of a recording medium placed on the span. Further preferably, at least a portion of the plurality of suction holes forms a row of holes arranged linearly so as to face the side end region of the trailing edge in the transportation direction of the recording medium placed on the span.
In this case, the side end of the leading edge or the trailing edge of the recording medium side in the transportation direction can be held against the belt.
Preferably, a plurality of rows of holes are arranged in the transportation direction of the recording medium so that the interval of suction holes in the transportation direction of the recording medium is substantially 1/an integer times the length of the recording medium in the transportation direction.
In this case, each suction hole formed along the transportation direction of the recording medium is located at an interval of xe2x80x9c1/an integer timesxe2x80x9d the length of the recording medium in the transportation direction. In the status where the recording medium is transported with the leading edge portion facing the suction holes, the trailing edge portion of the recording medium can also be made to face the suction holes. Therefore, generation of a curl can be suppressed with respect to both the leading and trailing edges of the recording medium. In other words, by setting only the leading edge portion of the recording medium to face the suction holes, the trailing edge portion of the recording medium can also be made to face the suction holes without having to confirm the trailing edge portion. As a result, generation of a curl at both the leading and trailing edge portions of the recording medium in the transportation direction can be easily suppressed.
Preferably, the suction holes of the transportation belt are formed to face a recording medium at an inward position remote from the side end of the transported recording medium by a predetermined distance.
Preferably, the suction chamber has a surface facing the transportation belt. A plurality of suction holes are formed at the surface of the suction chamber. The plurality of suction holes have a shape elongated in the running direction of the transportation belt, and are arranged apart from each other across the width direction of the transportation belt. Further preferably, the interval between each of the plurality of suction holes of the suction chamber is substantially equal to the interval of the plurality of rows of suction holes in the width direction of the transportation belt.
Preferably, the recording medium transportation apparatus of the present invention further includes image formation means to form an image on a transported recording medium located on the span.
By applying the recording medium transportation apparatus of the present invention to the recording medium transportation system of an image recording apparatus, a specific application of a recording medium transportation apparatus can be obtained to improve practical usage thereof. Furthermore, an image of high picture quality can be formed by the image recording apparatus.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.